Posterior corneal surface topographic changes after laser in situ keratomileusis are related to residual corneal bed thickness

ObjectiveTo determine whether ectasia after laser in situ keratomileusis (LASIK) is related to residual corneal bed thickness.DesignRetrospective noncomparative case series.ParticipantsThirty-two eyes of 16 patients with refractive errors of −4.00 to −18.00 diopters were examined.InterventionLASIK was performed. The topography of the posterior corneal surface was examined with the Orbscan slit scanning corneal topography/pachymetry system.Main outcome measuresThe difference in the elevation of posterior corneal surface regarding the best-fit sphere was measured.ResultsAfter surgery, mean bulge of 17.2 ± 7.2 μm was found in eyes with residual corneal bed of 250 μm or greater, whereas 41.0 ± 22.1 μm was seen in eyes with bed thickness less than 250 μm (t = 4.29; P = 0.000).ConclusionPosterior corneal bulge is correlated with the residual corneal bed thickness. The risk of ectasia may be increased if the residual corneal bed is thinner than 250 μm.